Identification and molecular characterization of a novel splice-site mutation (G1205C) in the SQSTM1 gene causing Paget's disease of bone in an extended American family

Paget's disease of bone (PDB) is a common late-onset bone disorder characterized by focal areas of abnormal bone remodeling. Positional cloning efforts resulted in the identification of seven genetic loci (PDB1-7) with putative involvement in the pathogenesis of PDB. Meanwhile, the PDB-causing gene from the PDB3 region on chromosome 5q35 has been identified as the SQSTM1 gene. All mutations identified in this gene so far are located in or close to the ubiquitin-associated (UBA) domain of the protein. In 2001, we reported genotyping results of genetic markers located in the PDB3 region in an extended American family, indicating the involvement of the PDB3 locus. Here, we report the identification of a novel mutation (G1205C) in the SQSTM1 gene in this family. The G1205C mutation is located in the splice donor site of intron 7 and reverse-transcription polymerase chain reaction experiments showed that the presence of the C allele results in the production of two abnormal mRNA transcripts. Translation of the first transcript would result in a protein that lacks amino acids 351-388, including 26 amino acids of the second PEST domain in addition to two amino acids of the UBA domain. The second mutant mRNA transcript could result in a truncated protein (390X) that lacks almost the complete UBA domain. PDB mutations that disrupt the function of the PEST domain of SQSTM1 have not been reported before, so probably the pathogenic effect of both transcripts resides in the disruption of the ubiquitin-binding properties of the protein.

Paget's disease is associated with changes in the immunohistochemical distribution of noncollagenous matrix proteins in bone

Paget's disease of bone is characterized histologically by abnormal architecture of bone matrix. Extensive areas of woven bone and numerous scalloped cement lines occur as a result of increased irregular remodeling. Noncollagenous proteins (NCP) play an important role in the organization and mineralization of bone matrix and promote distinct cell-matrix interactions necessary for normal remodeling. To gain insight into the pathological changes in the biochemical composition of Pagetic bone, the distribution of NCPs in the calcified matrix of bone from patients with known Paget's disease was compared to that of bone from normal healthy volunteers. Undecalcified plastic-embedded sections of bone were stained immunohistochemically using antibodies generated against several NCPs. In Pagetic and normal bone a similar distribution of osteopontin was observed at cement (reversal) lines, whereas significant differences were observed in the distribution of osteopontin in the matrix immediately adjacent to Haversian canals, where initial osteoclast recruitment and attachment occur. The differences in osteopontin distribution appeared to be related to the state and severity of the disease. Site-specific differences in the distribution of osteonectin, osteocalcin, and decorin were also observed between normal bone and cortical and periosteal de novo Pagetic bone, whereas the distribution of other matrix proteins, such as biglycan, was unchanged. We conclude that these site-specific changes in the biochemical distribution of NCPs in Pagetic bone probably reflect abnormal production and/or incorporation during bone remodeling and may lead to disorganized matrix assembly and mineralization as well as have profound effects on bone cell functions.

Comparative study of alendronate versus etidronate for the treatment of Paget's disease of bone

Alendronate, an aminobisphosphonate, is much more potent than etidronate, an older bisphosphonate, in inhibiting osteoclast-mediated bone resorption, and unlike etidronate, therapeutic doses of alendronate are not associated with abnormal mineralization. In the present study, we compared the effectiveness, safety, and tolerability of 6 months of daily oral administration of alendronate (40 mg) with those of etidronate (400 mg) in 89 patients with clinically active Paget's disease. The primary efficacy end point was the percent change in serum alkaline phosphatase. Other end points included changes in urinary deoxypyridinoline excretion, pain, functional impairment scores, and radiological osteolysis. Tetracycline-labeled bone biopsies were obtained for histomorphometric analysis from a subset of 43 patients at the 6-month visit. The alendronate-treated group had significantly greater decreases in both serum alkaline phosphatase (79% vs. 44%) and urinary deoxypyridinoline (75% vs. 51%) than the etidronate-treated group (P < 0.001 in both cases). Normalization of serum alkaline phosphatase was much more frequent in alendronate-treated patients (63.4% vs. 17.0%; P < 0.001). Alendronate was well tolerated and had a safety profile similar to that of etidronate. Histomorphometry revealed decreased bone turnover and no qualitative abnormalities, including no direct negative effects on bone mineralization, with alendronate treatment. One patient receiving etidronate developed frank osteomalacia. Alendronate appears to be a highly effective treatment for Paget's disease of bone that offers an important therapeutic advance over etidronate.

Interpretation of laboratory results in the elderly. 1. A clinician's guide to hematologic and hepatorenal function tests

An understanding of the normal aging process and its effects on common laboratory values is essential when evaluating the elderly patient. Although results of research to determine precise changes in values for this age-group in hemoglobin, hematocrit, white cell count, ESR, serum bilirubin and alkaline phosphatase, SGOT, and glomerular filtration have not been conclusive in most instances, some of the findings described here warrant consideration. We believe that the established normal ranges for these values do not need to be significantly modified for the elderly and that slight deviations from them are normal for the healthy patient. However, all abnormal test results should not be attributed to aging alone; the clinician might overlook the need for further diagnostic workup for possible serious disorders.